Gas turbine engines are used to power aircraft. Gas turbine engines typically include a compressor, a combustor, and a turbine. The compressor compresses air drawn into the engine and delivers high pressure air to the combustor. In the combustor, fuel is mixed with the high pressure air and is ignited. Products of the combustion reaction in the combustor are directed into the turbine where work is extracted to drive the compressor and, sometimes, an output shaft. Left-over products of the combustion are exhausted out of the turbine and may provide thrust in some applications.
At cruising speed, the flow of air to the engine passes through an opening in the engine nacelle to engine intake. The engine intake generally has a fan with a number of blades that rotate to work the air. Air flow, such as cross-wind, for example, that travels in a direction obtuse from the line of flight of the engine may result in laminar separation as the flow passes over portions of the nacelle. This laminar separation tends to create a pressure gradient within the air flow to the fan, causing variations in pressure along the fan blade.